Powder feeding device for spray coating powder

Abstract

A spraycoating powder feed apparatus includes a powder pump of which the direction of feed is reversible and a conduit switch configured to alternately link either of two powder conduits to a powder hookup of the powder pump as a function of the conveyance direction of the powder pump.

1. A spraycoating powder feed apparatus, comprising:
 a control unit; 
 a powder pump having a first powder hookup and a second powder hookup, and a reversible feed direction, the powder pump configured to pneumatically move powder from the first powder hookup to the second powder hookup, or to pneumatically move powder from the second powder hookup to the first powder hookup; 
 a conduit switch comprising at least three conduit connections, the conduit switch configured to alternately link a first conduit connection to either a second conduit connection or to a third conduit connection, wherein the first conduit connection of the conduit switch is connected to the second powder hookup of the powder pump; 
 a powder feed tube connected to the first powder hookup of the powder pump; and 
 a fluidizing unit fitted at a lower end of the powder feed tube, the fluidizing unit having at least one fluidizing air dispensing element porous to compressed air but impermeable to powder 
 wherein the powder pump and the conduit switch are switched by the control unit in a mutually dependent manner between
 a forward powder conveyance in which the first conduit connection of the conduit switch is exclusively linked to the second conduit connection but not to the third conduit connection, and 
 a reverse powder conveyance in which the first conduit connection of the conduit switch is exclusively linked to the third conduit connection but not to the second conduit connection. 
 
 
     
     
       2. The powder feed apparatus as claimed in  claim 1 , wherein between the first and the second powder hookups, the powder pump comprises at least one powder chamber fitted with two powder apertures each having one valve, and each connected to one of the first powder hookup and the second powder hookup; and
 said control unit, during said forward powder conveyance or during said reverse powder conveyance, is arranged for alternately applying vacuum or compressed air to said powder chamber for aspirating a dose of coating powder by vacuum through one of the two powder apertures into the powder chamber and thereupon expelling the dose of coating powder by compressed air out of the powder chamber and through the other powder aperture. 
 
     
     
       3. Powder feed apparatus as claimed in  claim 2 , wherein the valves are signal-driven valves. 
     
     
       4. Powder feed apparatus as claimed in  claim 1 , wherein the powder pump is affixed to the upper end of the powder feed tube and jointly with the feed tube constitutes one unit. 
     
     
       5. Powder feed apparatus as claimed in  claim 1 , wherein the control unit is configured to reverse the powder pump and to reverse the conduit switch together. 
     
     
       6. Powder feed apparatus as claimed in  claim 5 , wherein
 the switch positions of the powder pump and of the conduit switch are mutually dependent in a manner that in one direction of conveyance of the powder pump, 
 the first conduit connection of the conduit switch is linked to the second conduit connection but not to the third conduit connection, whereas in the mode of the opposite powder pump conveyance direction, the first conduit connection of the conduit switch is linked to the third conduit connection but not to the second conduit connection. 
 
     
     
       7. Powder feed apparatus as claimed in  claim 1 , wherein the control unit is configured to automatically drive the powder pump and the conduit switch as a function of at least one control signal. 
     
     
       8. A spraycoating powder feed apparatus, comprising:
 a powder pump having a first powder hookup and a second powder hookup, and a reversible feed direction, the powder pump configured to pneumatically move powder from the first powder hookup to the second powder hookup, or to pneumatically move powder from the second powder hookup to the first powder hookup; 
 a conduit switch comprising first through third conduit connections, the conduit switch configured to alternately link the first conduit connection to either the second conduit connection or to the third conduit connection, wherein the first conduit connection of the conduit switch is connected to the second powder hookup of the powder pump; 
 at least one powder tank; 
 a powder feed tube connected between at least one said powder tank and the first powder hookup of the powder pump; 
 a powder delivery conduit connected to the second conduit connection of the conduit switch for receiving fresh powder from at least one said powder tank; 
 a powder recovery conduit connected to the third conduit connection of the conduit switch for returning unused powder to at least one said powder tank; and 
 a control unit connected to the powder pump and the conduit switch for switching the powder pump and the conduit switch in a mutually dependent manner between
 a forward powder conveyance in which the first conduit connection of the conduit switch is exclusively linked to the second conduit connection but not to the third conduit connection, and the powder pump is configured to pneumatically move fresh powder from at least one said powder tank to the first powder hookup then to the second powder hookup, then to the powder delivery conduit via the conduit switch, and 
 a reverse powder conveyance in which the first conduit connection of the conduit switch is exclusively linked to the third conduit connection but not to the second conduit connection, and the powder pump is reversed to pneumatically move unused powder from the powder recovery conduit via the conduit switch to the second powder hookup, then to the first powder hookup, then to at least one said powder tank. 
 
 
     
     
       9. The powder feed apparatus as claimed in  claim 8 , wherein
 between the first and the second powder hookups, the powder pump comprises a powder chamber fitted with first and second powder apertures which are connected to the first powder hookup and the second powder hookup, respectively, and have first and second valves, respectively; 
 said control unit is configured for, during said forward powder conveyance, alternately applying vacuum or compressed air to said powder chamber for aspirating a dose of powder by vacuum through the first powder aperture into the powder chamber and thereupon expelling the dose of powder by compressed air out of the powder chamber and through the second powder aperture; and 
 said control unit is further configured for, during said reverse powder conveyance, alternately applying vacuum or compressed air to said powder chamber for aspirating a dose of powder by vacuum through the second powder aperture into the powder chamber and thereupon expelling the dose of powder by compressed air out of the powder chamber and through the first powder aperture. 
 
     
     
       10. The powder feed apparatus as claimed in  claim 9 , wherein
 between the first and the second powder hookups, the powder pump further comprises another powder chamber fitted with third and fourth powder apertures which are connected to the first powder hookup and the second powder hookup, respectively, and have third and fourth valves, respectively; 
 said control unit is configured for, during said forward powder conveyance, alternately applying vacuum or compressed air to said another powder chamber for aspirating a dose of powder by vacuum through the third powder aperture into said another powder chamber and thereupon expelling the dose of powder by compressed air out of said another powder chamber and through the fourth powder aperture; and 
 said control unit is further configured for, during said reverse powder conveyance, alternately applying vacuum or compressed air to said another powder chamber for aspirating a dose of powder by vacuum through the fourth powder aperture into said another powder chamber and thereupon expelling the dose of powder by compressed air out of said another powder chamber and through the third powder aperture. 
 
     
     
       11. The powder feed apparatus as claimed in  claim 10 , wherein
 said control unit is configured for, during each of said forward powder conveyance and said reverse powder conveyance, alternately applying vacuum to one of said powder chambers while applying compressed air to the other one of said powder chambers. 
 
     
     
       12. The powder feed apparatus as claimed in  claim 9 , wherein
 said valves are automatic valves configured to automatically open or close as a function of an excess pressure or vacuum at the respective apertures, without being directly driven by a signal from the control unit. 
 
     
     
       13. The powder feed apparatus as claimed in  claim 9 , wherein said valves are signal-driven valves connected to the control unit to open or close in response to a signal from the control unit. 
     
     
       14. The powder feed apparatus as claimed in  claim 9 , wherein
 said first valve is connected to a first end of the powder chamber and the second valve is connected to a second end of the powder chamber opposite to the first end, 
 when the first conduit connection of the conduit switch is linked to the second conduit connection but not to the third conduit connection,
 the first valve is open for the fresh powder from said at least one powder tank coming into the powder chamber while the second valve is closed so as to store the fresh powder in the powder chamber; and 
 the second valve is open for the fresh stored in the powder chamber being moved out while the first valve is closed. 
 
 
     
     
       15. The powder feed apparatus as claimed in  claim 14 , wherein when the first conduit connection of the conduit switch is linked to the third conduit connection but not to the second conduit connection,
 the second valve is open for the unused powder from the powder recovery conduit while the first valve is closed so as to store the unused powder in the powder chamber; and 
 the first valve is open for the unused powder stored in the powder chamber being moved out while the second valve is closed. 
 
     
     
       16. The powder feed apparatus as claimed in  claim 8 , wherein the powder pump is affixed to an upper end of the powder feed tube and jointly with the powder feed tube constitutes one unit. 
     
     
       17. The powder feed apparatus as claimed in  claim 16 , further comprising:
 a fluidizing unit fitted at a lower end of the powder feed tube and dipping into at least one said powder tank; 
 the fluidizing unit having at least one fluidizing air dispensing element porous to compressed air but impermeable to powder. 
 
     
     
       18. The powder feed apparatus as claimed in  claim 8 , further comprising:
 a fluidizing unit fitted at a lower end of the powder feed tube and dipping into at least one said powder tank; 
 the fluidizing unit having at least one fluidizing air dispensing element porous to compressed air but impermeable to powder. 
 
     
     
       19. The powder feed apparatus as claimed in  claim 8 , wherein the control unit is configured to automatically drive the powder pump and the conduit switch as a function of at least one control signal. 
     
     
       20. The powder feed apparatus as claimed in  claim 8 , wherein
 said at least one powder tank comprises a fresh powder tank and a recovered powder tank; and 
 said powder feed tube is arranged to connect to the fresh powder tank during said forward powder conveyance, and to the recovered powder tank during said reversed powder conveyance. 
 
     
     
       21. The powder feed apparatus as claimed in  claim 20 , further comprising:
 a powder sprayer connected to the powder delivery conduit and the powder recovery conduit; 
 wherein the control unit is configured to switch the powder pump and the conduit switch into the forward powder conveyance for supplying fresh powder from the fresh powder tank to the powder sprayer for spraying powder on an object, and to switch the powder pump and the conduit switch into the reverse powder conveyance for returning powder unused by the powder sprayer back into the recovered powder tank.